The invention relates to direct backlight modules, and in particular to direct backlight modules with transparent plates having microstructure to facilitate illumination uniformity.
FIG. 1a is a side view of a conventional direct backlight module. Some light emitting from illumination tubes 4 directly passes through a diffusion plate 8a and a diffusion sheet 7 to a liquid crystal display 2; the reminder is reflected by a reflecting plate 5 and then passes through the diffusion plate 8a and the diffusion sheet 7 to the liquid crystal display 2. To attain uniform brightness in the liquid crystal display 2, the diffusion plate 8a is formed of opaque resin. A great deal of light is, however, inevitably lost.
FIG. 1b is a side view of another conventional direct backlight module. As shown in FIG. 1b, the diffusion plate 8b is constructed by irregularly meshed dot distribution to provide an even brightness for the liquid crystal display 2. The dot distribution, however, reduces light transmission efficiency.
US Patent No. 2003/0184993, as shown in FIG. 1c, discloses a direct backlight module having a lens array 8d on a translucent substrate 8c as well as a diffusion sheet 7 disposed between a liquid crystal display 2 and illumination tubes 4. The light emitting from the illumination tubes 4 is condensed while passing through the lens array 8d. Further, the condensed light travels forward while diverging, and is then diffused by the diffusion sheet 7, and finally illuminates the liquid crystal display 2. Although this direct backlight module can help avoid the absorption of light, the light passing through the lens array 8d will crossly diverge such that a great deal of light will illuminate the liquid crystal panel 2 beyond the viewable angle. Thus, brightness on the liquid crystal display 2 cannot effectively be increased.